I feel like after switching my bumper the other day there is a slightly larger gap between the hood and grills.... I could just be imagining this but it does look like the grills can be swapped and have a different lip

actually yes they can. you have to make sure the tab slides into the proper location on the top and bottom. The gap you have could just be the front bumper needs to be slightly adjusted since you removed the 4 screws on top to change the grills. just play with them some to close the gap. I had to do the same

its most likely the bumper, everytime i take it off and put it back on its either a tighter fit or a loose one..as for the grilles if they snap in u cant really go wrong. and its not your hood since u didnt touch it